Patent GB-595077-A (GB)
Title: Improvements in or relating to alternating current circuit breaker systems
IPC: H01H33/59
Filed: 1945-01-19
Abstract: 595,077. Protective cut-out arrangements. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. Jan. 19, 1945, No. 1567. Convention date, June 12, 1942. [Class 38(v)] In an A.C. circuitbreaker system particularly for use on 60 cycles, and of which Fig. 1 shows in detail one phase C of one end of a line section, actuation of the circuit - breaker C B C therefor in response to a fault is controlled by one of an assembly of relays R through a synchronising device SC, whereby the circuit-breaker operating mechanism is energised at a time bearing a predetermined relation to the first current zero of the line current after the occurrence of the fault, the interrupting time of the circuitbreaker being a predetermined even number of complete half-cycles after the said first current zero. The device SC comprises a gas-filled, grid-controlled glow type tube 21 connected in series with the trip contacts TC of the relay R appropriate to phase C, a holding relay 50, and the trip coil TCC of circuit-breaker CBC. The grid 23 of tube 21 is biassed by a battery 26 to just above cut-off, an opposing bias in accordance with the line voltage being provided by a current transformer 30 through an impedance device, comprising a resistance 31 and inductance 32, and a full-wave rectifier 33, to render tube 21 non-conductive except at the zero-points of the rectified A.C. voltage wave, which owing to the values of the resistance 31 and inductance 32 leads the line current by a small angle (approx. 10 degrees) as shown in Fig. 2 by the curve V. Assuming a fault occurs at F in the line-current curve 1, relay R locates the fault and closes its contacts TC at the point G, Fig. 2, thereby applying plate voltage to tube 21 which will be rendered conductive to energise the tripping coil TCC at the point in the curve V corresponding to the point H in curve 1. Since operation of the circuit-breaker is impracticable within the short time H-Z, use is made of the more symmetrical following half - cycles, the operating time of the circuit-breaker being adjusted by means, such as a resistance 36, to correspond with the time H-Z3, or H-Z5. Protection against failure of the tube 21 is afforded by a delayed-action tripping relay 37. In addition a test-panel T is provided wherein operation of a pressbutton PB energises a relay 41 to bypass tube 21 and connect it to a test-circuit 47, relay 37 remaining operative in the event of a fault occurring during test. The curve V in Fig. 2 may be in phase with, or lag behind, the line current, in which cases, the synchronising point H would coincide with the point Z, or be retarded to H<1>, respectively. Fig. 4 shows a modification of the timing means incorporating a low-inertia relay 52 capable of closing its contacts 54 at each zero-point in its magnetising current. When a fault occurs, a relay 60 is energised to permit current from a current transformer 61 to flow in a timing circuit comprising an inductance 64, a high-voltage current transformer 65 and an auxiliary relay 66 shunted by a resistance 69 and the relay 52. The latter is thus energised by two voltages, one obtained from the secondary of transformer 65 and in phase with the line current, and the other obtained from the voltage drop in the inductance 64 leading the line current by 90 degrees. When the point H is reached, the leading and in-phase currents become equal whereupon relay 52 closes its contacts 54 and energises the tripping coil 57. In a further modification, Fig. 5, a fault-responsive relay 60<1> normally shorts part 251 of a potentiometer 25 thereby impressing the full voltage of biassing battery 26 on the grid 23 of synchronising tube 21<1>. When a fault occurs, contacts 621 of relay 601 open and decrease the bias so that tube 21<1> is rendered conductive at the first current zero in the A.C. wave supplied through rectifier 33, as in Fig. 2, except that due to the omission of the phase-advancing impedance 31-32, the point H is moved into coincidence with Z. A voltage-limiting grid-glow tube 30<1> cuts off the voltage peaks applied to rectifier 33.